/* Copyright 2008 dnAnalytics Project.
 *
 * Contributors to this file:
 * Jurgen Van Gael
 * Marcus Cuda
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 * 
 * * Redistributions of source code must retain the above copyright notice, this 
 *   list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above copyright notice, 
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 * * Neither the name of the dnAnalytics Project nor the names of its contributors
 *   may be used to endorse or promote products derived from this software without
 *   specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
 * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

namespace dnAnalytics.Math
{
    public partial class SpecialFunctions
    {
        ///<summary>Calculates the inverse error function evaluated at z.</summary>
        /// <returns>The inverse error function evaluated at given value.</returns>
        /// <remarks>
        /// 	<list type="bullet">
        /// 		<item>returns Double.PositiveInfinity if <c>z &gt;= 1.0</c>.</item>
        /// 		<item>returns Double.NegativeInfinity if <c>z &lt;= -1.0</c>.</item>
        /// 	</list>
        /// </remarks>
        ///<summary>Calculates the inverse error function evaluated at z.</summary>
        ///<param name="z">value to evaluate.</param>
        ///<returns>the inverse error function evaluated at Z.</returns>
        public static double ErfInv(double z)
        {
            if (z == 0.0)
            {
                return 0.0;
            }

            if (z >= 1.0)
            {
                return double.PositiveInfinity;
            }
            if (z <= -1.0)
            {
                return double.NegativeInfinity;
            }

            double p, q, s;
            if (z < 0)
            {
                p = -z;
                q = 1 - p;
                s = -1;
            }
            else
            {
                p = z;
                q = 1 - z;
                s = 1;
            }
            return ErfInvImpl(p, q, s);
        }
    }
}
